Device for the dehydration of sewage sludge

ABSTRACT

A method and apparatus for dehydrating sewage sludge is described. Sewage sludge is placed into a dehydration chamber. The sewage sludge is heated to convert moisture in the sewage sludge to steam and cause gasification. Steam and gases are drawn from the dehydration chamber into a condenser, where the steam is condensed to form hot water. Gases are drawn from the condenser to a burner.

The invention concerns a method and a device for the dehydration ofsewage sludge, in particular the sludge which accumulates in municipalsewage plants.

BACKGROUND OF THE INVENTION

The fresh or decayed sludge which accumulates in large volumes in suchsewage plants consists of less than 10% solid matter. To be utilized oreliminate, this sludge must first be dehydrated. Through mechanicaldehydration methods, such as suction cell filtering, sludge is reducedto a consistency of about 30% solid matter; thus it is still composedmainly of water.

SUMMARY OF THE INVENTION

What is required is an improved apparatus for dehydrating sewage sludge.

The process which has been developed to meet the need outlined above isas follows: radiant heat and hot air are produced simultaneously throughthe combustion of heating oil or gas. Then the radiant heat acts on thesewage sludge while it is being conveyed mechanically. At the same time,the sewage sludge undergoes an indirect heat exchange with the hot air.

According to another aspect of the invention there is provided anapparatus for dehydration of sewage sludge, which is comprised of adehydration chamber having an intake opening and a discharge opening.Mechanical conveyance means is used to convey sewage sludge from theintake opening to the discharge opening. A plurality of radiant heaterswith burners disposed in side by side relation, each of the radiantheaters having heat radiation surfaces disposed within the dehydrationchamber which radiate heat at temperatures in excess of 850 degreescentigrade, whereby sewage sludge is heated to convert moisture in thesewage sludge to steam and most harmful organic compounds contained inthe sewage sludge are broken down. A condenser adjoining the dehydrationchamber, means being provided to draw steam from the dehydration chamberinto the condenser, whereby the steam is condensed to form hot water andgases. A gas vent pipe diverting gases from the condenser to one of theburners of the radiant heaters, whereby the gases are heated totemperatures in excess of 1700 degrees centigrade thereby breaking downharmful dioxins contained in the gases.

In the thermal sludge dehydration process described polluted air isdrawn through the incineration zone so that the pollutants can be burnedand wet sewage sludge, whether free or decayed, is reduced to asolid-matter consistency of more than 95%. Further advantages in thisnew process and device can be seen from the following description.

The process which has been developed to meet the need outlined above isas follows: radiant heat and hot air are produced simultaneously throughthe combustion of heating oil or gas. Then the radiant heat acts on thesewage sludge while it is being conveyed mechanically. At the same time,the sewage sludge undergoes an indirect heat exchange with the hot airwhich has been generated. The vapours produced from the sludge are thensuctioned off from the space above the sludge and are condensed. As aresult of the effect of heat radiation and the simultaneous transfer ofheat from the hot air to the wet sewage sludge, considerable dehydrationis already taking place, e.g. from less then 10% solid content tobetween 50 and 90%. In the process, a considerable volume of steam isproduced. The volatile organic pollutants, such as hydrocarbons anddioxins, given off by the sludge as it is being mechanically moved, arecracked or broken down due to the influence of heat radiation during thesteam phase. The products of cracking or disintegration are on the wholeharmless and therefore--so long as they condense with the vapours--donot pollute the condensate. Disintegration of the sludge throughoxidation is not possible, the steam thus generated being almostcompletely free of oxygen, so that the sludge does not come into contactwith oxygen.

In the recommended method of carrying out the process, the sludge whichhas been partially dried by means of radiant heat in the first stageundergoes a second, and possibly further, drying stages, by means ofmechanical conveyance and indirect heat exchange using the hot airgenerated. Vapours produced in the second and any subsequent dryingstages are drawn off with a stream of warm air and condensed. While inthe first (open) stage, only vapours are drawn off into the condenser bymeans of an air stream, in subsequent stages steam produced from thesludge is also drawn off in this manner. For this purpose, hot air whichhas been partially cooled through the exchange of heat in the second andany subsequent stages is used as the warm air stream for the removal ofthe vapours produced in these stages. It is recommended that the airstream remaining after the vapours have condensed be utilized ascombustion air in the burning of heating oil or gas, so that anypollutants contained in the air stream can be burned.

In the recommended procedure, a heat exchange is carried out between thehot air produced by burning the heating oil or gas at a temperature of500 to 850 degrees C., and the sewage sludge. This heat exchange isnecessarily indirect, so that the sludge does not come into contact withair and, once the sludge has been almost completely dried, no oxidativedisintegration can occur.

The sewage sludge is moved in two consecutive stages in oppositedirections, generally in a straight line. By mounting the levels on topof each other and moving the sludge in alternate directions, it ispossible to carry out the dehydration on a comparatively small surfacearea, so that the device can be mounted on a vehicle.

In the first stage of this process, organic compounds, in particularhydrocarbons and/or dioxins, which has been released from the sewagesludge, are cracked in the steam phase by radiant heat at temperaturesof about 850 to 1200 degrees C. A particular feature of this process isthe high temperatures produced during the steam phase--ranging ingeneral between 800 and 2300 degrees C., and optimally between 900 and1150 degrees C.--and the fact that at the same time there is no contactwith the oxygen of the air, the result being that the sludge releasesits water quickly without oxidative disintegration, and also that thepollutants which were released from the sludge into the steam at thatphase in the process are cracked or broken down into less toxic orharmless compounds.

It is recommended that the vapours which developed in the first stage bedrawn into the condenser by means of low pressure. One way to keep thepressure of the condenser low is to place a suction draught fan on theopposite side of the condenser. The gases remaining after condensationcan be filtered and then used for burning heating oil or gas. In orderto obtain an extensive vapour condensation, condensation is carried outby means of heat exchange, using water which has been cooled in a deepfreeze unit during the cycle.

Other devices used in the process are: several heat radiators, placedside by side, each with a combustion chamber in which the lower wall isconstructed as a heat radiation surface, and with a heating oil or gasburned in each combustion chamber, and a heat exchanger for heating theair with the hot combustion gases situated, in a dehydration chamberunderneath the heat radiation surfaces; open conveyor systems, whichextend more or less from one end of the radiation zone of the heatradiator to the other end, thus allowing for the indirect heating of thesewage sludge by means of hot air; and a condenser, which is connectedwith the dehydration chamber by a pipe. The device consists thereforeprincipally of: heat radiators, which produce hot air in addition toradiating heat; the sewage sludge conveyor systems, which convey thesewage sludge past the heat radiation zone, subjecting it to radiantheat, so that it releases water in the form of steam; and the condenserfor condensing the steam generated in this process. It is alsosignificant that the heat exchanger and heat radiator are integrated,and together form a compact unit, so that a mobile dehydrator can beequipped with several such heat radiators. The heat radiates in aconical shape from each radiator. Therefore, the placing of several heatradiators in a row allows for a much longer radiation zone, along whichthe sewage sludge conveyors are arranged longitudinally.

It is recommended that the sewage sludge conveyor consist of severaltroughs placed side by side in a parallel arrangement, with conveyoraugers revolving in the troughs, and that the troughs be fitted with acasing and the augers with a hollow shaft for heating with the hot air.The hot air which is generated in the heat exchanger that surrounds theradiator combustion chambers like a ring is used for heating thesetroughs augers, by conducting the air, which has been heated to 850degrees C., first through the trough casing and then, in the oppositedirection, through the hollow shaft of the auger. It is recommended thatfor this procedure suction tubes fitted with openings be fastened alongthe sides of the troughs, and that these be connected to the condenser.These suction tubes are kept at low pressure by the condenser, so thatthe vapours given off by the sewage sludge are drawn up into the suctiontubes and from there into the condenser.

A further refinement of the device consists of the placing of at leastone and preferably two levels of closed sewage sludge conveyor systemsunderneath the open conveyor system, their path being much the same asthat of the open system, and each level moving the sludge in theopposite direction from the ones above and below it. In the closedconveyors the partially dehydrated sewage sludge is dried still morethan a consistency of at least 95% and, optimally, of at least 98% solidmatter. The multi-level arrangement of the conveyors on top of eachother allows for a compact structure which occupies a comparativelysmall space. In this recommenced design, the closed conveyors consist oneach level of several parallel pipes containing rotating augers. Thepipes are fitted with a casing and the conveyor augers with a hollowshaft for the hot air heating process, and along the length of each pipea suction tube is mounted and connected to the pipe's inner chamber bymeans of openings which are connected at one end to the centralbore-hole of the hollow shaft or the casing of the pipe in question andon the other end to the condenser. Each conveyor level can consist offrom five to about fifteen, optimally of eight to twelve, troughs orpipes. The heating of the pipes is carried out in the same manner as theheating of the troughs, in that the hot air from one of the heatradiators is conducted into a level of pipe augers. From the auger, thehot air is first conducted through the pipe casing, then through thehollow shaft into the suction tube and finally into the condenser. Thevapours produced in the pipes pass through the openings in the suctiontube and are carried by the air stream into the condenser, where theyare condensed.

It is recommended that in this method each trough and the pipes lyingunderneath it be joined by connecting pipes placed alternately at bothends, so that the sewage sludge is conveyed in alternate directionsthrough the trough and the pipes.

The connecting pipes on the lowest level of auger pipes are mounted ontothe discharge auger, which is located at a 90 degree angle to the augerpipes above it. The lowest level of pipes, which may consist of about 10auger pipes, delivers the dried sludge through the connecting pipes intothe discharge auger, from which the dried sludge is then expelledsideways.

The conveyor augers are mounted onto drives, and the rotating speed ofthe motors of any one level of augers can be controlled independently ofthat of the others. In this manner, it is possible to set a differentprocessing time for the sewage sludge in the trough level than in thelower auger level, that is, each level may be adjusted separately tosuit the type of sludge or the speed of vaporization.

It has also been designed so that the feeding device can be placed atone end of the dehydration chamber, protruding from the chamber wall,and connected on the intake side with a loading funnel, and on thedischarge side over the intake end of the open sludge conveyor. One wayof loading the sludge through the funnel would be with conveyor belt. Itis recommended that there be an equal number of feeding augers--thesecould be pipe augers--as there are troughs. By this method, each feedingauger is placed together with a trough. This feeding augers can also beheated by means of the warm air discharged from the hollow shaft of therespective trough auger.

It is recommended that the device be mounted on a chassis. In this wayit is possible to transport the portable device from place to place bymeans of a vehicle such as a semitrailer. In this way, even small sewageplants, where a lesser volume of sludge requires only occasionaldehydration, can take advantage of this new process.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention is illustrated by the following diagrams:

FIG. 1 shows a simplified flow chart of the new process;

FIG. 2 shows a simplified flow chart of the air intake and dischargesystem in the new process;

FIG. 3 shows a simplified section view of the heat radiator as used inthe new process;

FIG. 4 shows an overall diagram of the new device;

FIG. 5 shows a three-dimensional drawing of the trough auger used in thedevice;

FIG. 6 shows a three-dimensional drawing of the pipe auger used in thedevice, with a portion of the outer casing cut away;

FIG. 7 shows a three-dimensional drawing of an alternate embodiment ofthe invention;

FIG. 8 shows a simplified drawing of the pipe system of the alternateembodiment;

FIG. 9 shows a three-dimensional view of the top trough auger used inthe alternate embodiment; and

FIG. 10 shows a three-dimensional view of the lower trough auger used inthe alternate embodiment, with a portion of the outer casing cut away.

DETAILED DESCRIPTION OF THE INVENTION

The diagram in FIG. 1 illustrates the important stages in the newprocess and is self-explanatory.

The operation of the embodiment illustrated in FIG. 4, will hereinafterbe described. Heat is radiated from all radiators onto the top troughauger. The hot air produced by any one radiator is directed to only oneauger level, for example the trough augers or one or the other levels ofpipe augers. The air first flows through the casing of the auger andthen enters the bore-hole of the auger shaft from the casing. In thecase of the trough augers, the hot air is discharged from the augershaft and into the intake auger, in order to heat it up as well. As thishot air was only exchanged indirectly with the sludge, it does notcontain any pollutants and can be discharged into the atmosphere on theother end of the intake auger. One method is to mix it with smoke andconduct it into the chimney. The vapours produced in the trough augerare drawn through the suction tube into the condenser and thencecondensed.

In the case of the pipe auger, the hot air again enters the casing firstand passes from there into the auger shaft. Then the still warm airflows through the suction tube of the auger and conveys the vapoursgiven off from the sewage sludge into the condenser. After the vapourshave been condensed, the remaining air is used for burning in the heatradiators.

FIG. 3 shows a heat radiator (1) for the production of infraredradiation and hot air, to be used in this innovative dehydration device.The heat radiator has a heating oil burner (2), to which heating oil isconducted through a pipe (3) and combustion air through another pipe(42). The burner (2) is covered with a hollow casing (2a) which has anopening to the combustion chamber (4). This casing receives dischargeair from the vapour condenser (18) via pipe (41). The temperature in thecombustion chamber (4) can be as high as 1700 degrees C. The metallicradiation cone (5) radiates heat downward, resulting in temperaturesunder the cone of up to 1200 degrees C. The radiation cone (5) issurrounded by a blunt conical reflection shield (6), which bundles theheat radiation. The chamber (4) is surrounded by another chamber (7),through which the hot combustion gas flows from combustion chamber (4).Chamber (7) contains a helical pipe (8), which is connected to an airfan (9). The fan (9) draws in air from the surrounding area and forcesit through the heat exchanger (8, 7). The hot air thereby generatedexits from the heat exchanger (10) at a temperature of up to 850 degreesC., optimally between 600 and 800 degrees C.

The newly invented device shown in FIG. 4 is mounted on a semi-trailerchassis (40), which can be towed by a tractor. The device contains threeheat radiators (1), which radiate heat conically (5) onto thedehydration chamber (11) below. In the dehydration chamber (11), tentrough augers (12) are placed along the side of the vehicle and aredriven by electric motors (13). Each trough auger (12) is supplied by anintake auger (14), which is likewise driven by an electric motor (15).The row of intake augers (14) takes up the wet sewage sludge from asupply funnel (16) and conveys it to a connecting pipe (17), throughwhich the sludge is forced into the auger trough (12). In trough (12),the wet sewage sludge is exposed directly to the heat from the threeradiators (1). In addition, the trough (12) and the auger shaft areheated by the hot air, as will be explained in more detail below. Thewet sewage sludge is conveyed through the auger of the trough to theother end of the pipe, rotated about, and dehydrated to a considerableextent. The vapours released in this process are drawn up into a suctiontube, which will be described in greater detail below, and from thereconducted into a condenser (18), where they are condensed.

The partially dehydrated sewage sludge passes through the connectingpipe (19) into the auger pipe (20), the auger being driven by anelectric motor (21). In the auger pipe (20), the partially dehydratedsewage sludge is conveyed forward again to a connecting pipe (22). Theauger pipe (20) is heated by means of hot air from the middle heatradiator (1), so that the dehydration process continues as the sludge isconveyed to connecting pipe (22). The vapours produced during thisprocess are drawn up by means of a warm air stream through the suctiontube into pipe (20), which is described in greater detail below, arealso fed into the condenser (18), where they are condensed.

The now highly dehydrated sewage sludge passes through the connectingpipe (22) into the auger pipe below (23), in which the sludge is almostcompletely dehydrated, i.e. it is dried to a consistency of about 98%solid matter. The auger of the pipe (23) is also driven by an electricmotor (24), which conveys the sludge backward to connecting pipe (25).The dry sludge is forced through the connecting pipe (25) into thedischarge auger (26), which is placed at a 90 degree angle, and whichdischarges the dehydrated sludge laterally from the device. On both endsof both the auger through (12) and the auger pipes (20, 23) air boxes(27) are provided to conduct the air, as shown in detail in FIG. 2, arein particular to direct it from the casing into the bore-hole of thehollow shaft.

The auger trough (12) which is shown in FIG. 5 in simplified form, has ahollow casing (28), through which the hot air generated from a heatradiator (1) is drawn. The hot air discharged from casing (28) entersthe bore-hole (29) of the auger shaft (30a), as shown by the arrow, andthere heats up auger (30). A suction tube (31) is connected to the augertrough (12), which is provided with row of openings (32) on the side ofauger (30). The suction tube (31) leads to the condenser (18) (notshown), which is kept at a low pressure, so that the vapours releasedfrom the sewage sludge in trough (12) are drawn into the condenserthrough the openings (32) and the suction tube (31).

The auger pipe (20) shown in FIG. 6 is identical to auger pipe (23) andother augers pipes which, if needed, could be placed on a fourth level.The auger pipe (20) has a hollow casing (33) in which a suction tube(34) is separated by radial walls (35). The auger shaft (36a) of auger(36) is also provided with a bore-hole (37) for heating purposes. In thearea of the suction tube (34), the inside wall (38) of pipe (20) isfitted with openings (39) over its entire length. Through these openings(39), the sewage sludge discharges its vapours into the suction tube.The hot air used to heat the auger pipe (20) is first conducted from aheat radiator (1) into the pipe casing (33), in the direction shown bythe arrow, and from there into bore-hole (37) of the auger shaft (36a),and finally into the suction tube (34), through which the vapours aredrawn off and conveyed by an air stream into the condenser (18).

The alternate embodiment illustrated in FIGS. 7 through 10, representsan improved embodiment of the invention. Along with modifications whichwill hereinafter be described, this embodiment is capable of attaininghigher temperature levels. The alternate embodiment has been modified toalter the method by which a heat exchange is effected within the troughauger. Flexibility has also been provided as to whether the heattransfer is effected using hot water or not exhaust gases. FIG. 2 showsschematically the movement of sewage sludge, the flow of hot exhaustgases, the flow of steam and toxic gases, and the circulation of hotwater within the system, as will be hereinafter described. Referring toFIGS. 7 and 8, there is illustrated an apparatus for dehydration ofsewage sludge. The alternate embodiment has a dehydration chamber whichis enclosed by insulating walls 110 and 123. The dehydration chamber isactually divided into two smaller chambers, a heat chamber 116 and asteam chamber 118. The dehydration chamber has an intake opening 103 anda discharge opening 127. A plurality of troughs 117, 120, and 121 aredisposed in levels within dehydration chamber 118. Trough 117 ispositioned within heat chamber 116 and troughs 120 and 121 arepositioned within steam chamber 118. Each trough has rotatably mountedaugers 129, for mechanically conveying sewage sludge. Sewage sludge isthereby moved from intake opening 103 through a series of augers todischarge opening 127. Troughs 117, 120, and 121 are arranged within thedehydration chamber on a number of levels; a top level--trough 117, amiddle level--trough 120 and a lower level--trough 121. Each of levelhas substantially the same conveyance path which moves sewage sludge inalternating directions from level to level in sequence. This isaccomplished through the use of a plurality of transfer boxes. As sewagesludge enters intake opening 103 it is conveyed by along an auger trough104 to a transfer box 109, where the sewage sludge is transferred fromauger trough 104 on an entry level to auger trough 117 on the top level.Sewage sludge is then conveyed along auger trough 117 to transfer box124, where the sewage sludge is transferred from auger trough 117 on thetop level to auger trough 120 on the middle level. Sewage sludge is thenconveyed in the opposite direction along auger trough 120 to transferbox 112, where the sewage sludge is transferred from auger trough 120 onthe middle level to auger trough 121 on the lower level. A furtherchange in direction then occurs and sewage sludge is conveyed alongauger trough 121 to transfer box 126, where the sewage sludge istransferred from auger trough 121 on the lower level to dischargeopening 127. Referring to FIGS. 9 and 10, each trough has a hollowsidewall 131 defining a fluid flow passage 130. There is a difference inconstruction between trough auger 117 and trough augers 120 and 121.Trough auger 117 is illustrated in FIG. 9. Trough augers 120 and 121 aresimilar in construction and this construction is illustrated in FIG. 10.A plurality of radiant heaters 115 with burners 135 are disposed in sideby side relation within heat chamber 116. Each of radiant heaters 115have heat radiation surfaces disposed within heat chamber 116 whichradiate heat at temperatures in excess of 850 degrees centigrade. In thealternate embodiment, the maximum temperature of the radiation surfaceis 1600 degrees. The preferred operating temperature is 1250 degrees.The sewage sludge is heated to convert moisture in the sewage sludge tosteam and cause gasification. At the described temperatures the mostharmful organic compounds contained in the sewage sludge are brokendown. The distance between the radiation surfaces of heaters 115 and thesewage sludge on top auger trough 117 is 10 centimeters at its closestpoint and averages 35 centimeters. As is illustrated in FIG. 9, topauger trough 117 has a cut out at the top with a circular area of about70 degrees. As a result approximately 67% of top auger trough 117 isexposed to the energy source and subjected to infrared rays. The darkgrained surface of the sewage sludge allows a high rate of absorption ofradiant energy from heaters 115. Auger troughs 104, 117, 120, and 121,have motors 105, 107, 108, and 111, respectively which rotate auger 129.Auger 129 is a special spiral auger with a relatively high revolutionrate. It conveys sewage sludge along the auger troughs at 40 to 60revolutions per minute. The sewage sludge in the conveying pipe isconstantly turned and moved to prevent the premature "baking" of thematerial. A condenser 125 adjoins the dehydration chamber. There is afree flow a steam from heat chamber 116 to steam chamber 118. Steam isdrawn via steam ducts 122 from dehydration chamber 118 into condenser125. As is best illustrated in FIG. 10, troughs 120 and 121 haveconnecting steam ducts 132. Steam from heat chamber 116 can enter steamducts 132 via the opening defined by flanges 133. Steam ducts 132 areconnected to steam ducts 122. In condenser 125 steam is condensed toform hot water and gases. The steam enters condenser 125 fromunderneath. A "barrel condenser" process is used wherein the steam issprayed with cold water from tank 128 in order for it to condense. Theresulting function in volume and the closed system of the steam ducts122 and 132 causes a significant under pressure. The developing vacuumsuction draws steam and gases out of steam chamber 118 via steam ducts122 and 132. In order to stabilize and secure this operation a suctionfan is installed at the end of each lower steam duct. The hot waterwhich is condensed flows through hot water pipe 136 to valve 137. Valve137 provides the operator with the option of collecting hot water in hotwater tank 138 or redirecting the flow of hot water through pipe 139 forexternal use. This water is substantially free of pollutants. As theheat in heat chamber 116 and steam chamber 118 causes a gasification ofthe sewage sludge to occur, gases are drawn into condenser 25 along withsteam. The gases produced include methane, and depending upon the natureof the sewage sludge may carry dioxins. These gases are diverted via agas vent pipe 134 from condenser 125 to one of burners 135 of radiantheaters 115. In burner 135 the gases are burned at temperatures inexcess of 1200 degrees centrigrade thereby breaking down harmful dioxinscontained in the gases. In the alternate embodiment, the burner flamesreach temperatures of 1900 degrees. Exhaust gases from burners 135 areultimately released through chimney 113. However, the exhaust gases fromburners 135 have a temperature of 850 degrees and are therefore avaluable source of potential energy. For this reason each of burners 135have an exhaust gas pipe 155 which connects with an exhaust gasdistribution box 119. Exhaust gas distribution box 119 serves to connecteach one of exhaust gas pipes 155 with fluid flow passage 130 from oneof trough augers 117, 120, or 121. After flowing through fluid flowpassages 130 of the respective trough augers the exhaust gases arecollected at an exhaust gas collection box 114 which is connected tochimney 113. Similarly, the hot water produced by condenser 125 is asecondary source of energy and is connected to a system for circulationof the hot water. For reasons of convenience the hot water is firstaccumulated in hot water tank 138. A first fluid flow line consisting ofpipes 140 and 142 connects condenser 125 via hot water tank 138 withfluid flow passage 130 defined by the hollow sidewall 131 in augertrough 104. This permits a heat exchange to occur transferring heat fromthe hot water to the sewage sludge. The circulation of hot water throughthe first fluid flow line is completed by pipes 144. On pipe 144 is avalve 145 which gives the operator the option of directing the return ofwater through radiator 149, and pipe 150 to cold water tank 128, or todivert the water for external use through pipe 146. It must beappreciated that the system will always be producing a surplus of waterwhich must be periodically removed from the system. A second fluid flowline indirectly connects the exhaust of the burners 135, via chimney113, with fluid flow passage 130 defined by hollow sidewall 131 of augertrough 104. Second fluid flow line consists of pipes 143, and 142 whichrepresent an inflow of hot exhaust gases from chimney 113 to fluid flowpassage 130 of auger trough 104. Pipes 144 and 148 which represent anoutflow of exhaust gases from auger trough 104 back to chimney 113. Ofcourse, hot water and hot exhaust gases cannot be used at the same timeto preheat auger through 104. The operator makes a selection as to whichsource of energy for preheating he wishes to use by adjusting valves 141and 147. Valve 141 controls whether hot water or gas has access to pipe142 leading into fluid flow passage 130 of auger trough 104. Valve 147controls whether fluids returning from auger trough 104 are directed tocold water tank 128 or to chimney 113. Water tank 128 has twocompartments, a small holding compartment 154 and a larger holdingcompartment which has greater capacity 152. Compartments 154 and 152 areconnected by an overflow pipe 151. A line 153 goes from compartment 152into the top of condenser 125, for use in the condensation of steam ashas previously been described. The system is compact enough to bemounted on a trailer 101, which has an operator control area 102.

The embodiments of the invention in which an exclusive property orpriviledge is claimed are defined as follows:
 1. An apparatus fordehydration of sewage sludge, comprising:a. a dehydration chamber havingan intake opening and a discharge opening; b. a plurality of troughs inwhich are rotatably mounted augers, the troughs being disposed in thedehydration chamber for mechanically conveying sewage sludge from theintake opening to the discharge opening, the troughs being arrangedwithin the dehydration chamber on a number of levels, each level havingsubstantially the same conveyance path which move sewage sludge inalternating directions from level to level in sequence, each troughhaving a hollow sidewall defining a fluid flow passage; c. a pluralityof radiant heaters with burners disposed in side by side relation, eachof the radiant heaters having heat radiation surfaces disposed withinthe dehydration chamber which radiate heat at temperatures in excess of850 degrees centigrade, whereby sewage sludge is heated to convertmoisture in the sewage sludge to steam, cause gasification and breakdownharmful organic compounds contained in the sewage sludge; d. a condenseradjoining the dehydration chamber, means being provided to draw steamand gases from the dehydration chamber into the condenser, whereby thesteam is condensed to form hot water; e. a gas vent pipe diverting gasesfrom the condenser to one of the burners of the radiant heaters, wherebythe gases are burned at temperatures in excess of 1700 degreescentigrade thereby breaking down harmful dioxins contained in the gases;f. a first fluid flow line connecting the condenser with the fluid flowpassage defined by the hollow sidewall, whereby hot water from thecondenser is directed through the fluid flow passage; g. a second fluidflow line connecting an exhaust port of one of the burners with thefluid flow passage defined by the hollow sidewall, whereby hot exhaustgases from one of the burners of the radiant heaters are directedthrough the fluid flow passage; and h. valves on the first fluid flowline and the second fluid flow line, whereby a selection may be made asto whether fluids from the first fluid flow line or second fluid flowline are directed through the fluid flow passage to effect a heatexchange with sewage sludge being carried by the auger.
 2. An apparatusfor dehydration of sewage sludge, comprising:a. a dehydration chamberhaving an intake opening and a discharge opening; b. a trough in whichis rotatably mounted an auger for conveying sewage sludge from theintake opening to the discharge opening, the auger having a hollow shaftdefining a fluid flow passage whereby preheated fluids are passedthrough the fluid flow passage to effect a heat exchange with sewagesludge being carried by the auger; c. a plurality of radiant heaterswith burners disposed in side by side relation, each of the radiantheaters having heat radiation surfaces disposed within the dehydrationchamber which radiate heat, whereby sewage sludge is heated to convertmoisture in the sewage sludge to steam and cause a gasification; d. acondenser adjoining the dehydration chamber, means being provided todraw steam and gases from the dehydration chamber into the condenser,whereby the steam is condensed to form hot water; e. a gas vent pipediverting gases from the condenser to one of the burners of the radiantheaters, whereby the gases are burned; and f. a first fluid flow lineconnecting the condenser with the fluid flow passage, whereby hot waterfrom the condenser is directed through the fluid flow passage.
 3. AnApparatus as defined in claim 2, wherein a second fluid flow lineconnects an exhaust port of one of the burners with the fluid flowpassage, whereby hot gases from the exhaust port is directed through thefluid flow passage.
 4. An Apparatus as defined in claim 2, wherein asecond fluid flow line connects an exhaust port of one of the burnerswith the fluid flow passage defined by the hollow sidewall, and valvemeans are provided for selecting whether hot gases from at least one ofthe exhaust port and the hot water from the condenser are directedthrough the fluid flow passage.
 5. In an apparatus for dehydration ofsewage sludge consisting of a dehydration chamber (11) having an intakeopening (17) and a discharge opening (25), mechanical conveyance meansfor conveying sewage sludge from the intake opening (17) to thedischarge opening (25), a plurality of radiant heaters (1) with burners(2) disposed in side by side relation, each of the radiant heaters (1)having heat radiation surfaces (5) disposed within the dehydrationchamber (11) which radiates heat whereby sewage sludge is heated toconvert moisture in the sewage sludge to steam and cause gasification, acondenser (18) adjoining the dehydration chamber (11), means (31 and 32)being provided to draw steam and gases from the dehydration chamber (11)into the condenser (18) whereby the steam is condensed to form hotwater, and a gas vent pipe (134) diverting gases from the condenser (18)to one of the burners (2) of the radiant heater (1) whereby the gasesare burned,wherein the improvement comprises said mechanical conveyancemeans being in the form of a spiral auger (129) disposed in a trough(117) such that sewage sludge in the trough (117) is exposed to radiantheat, the trough (117) having a hollow sidewall (131) defining a fluidflow passage (130) whereby preheated fluids are passed through the fluidflow passage (130) to effect a heat exchange with sewage sludge incommunication with the hollow sidewalls (131) of the trough (117), and afluid flowline connects the condenser with the fluid flow passagewhereby hot water from the condenser is directed through the fluid flowpassage.